This invention relates to an improved exhaust system for watercraft and more particularly to an improved exhaust system for a personal watercraft incorporating a water-cooled engine.
There is a particularly popular type of small watercraft which is characterized as a "personal watercraft." This type of watercraft is a type in which one or more passengers ride on rather than in the watercraft. Frequently, these watercraft are sporting in nature, and the occupants or riders expect to leave the watercraft at times during its use and enter into the body of water in which the watercraft is operating. Generally, this type of watercraft is also powered by a jet propulsion unit which is positioned in a tunnel formed on the underside of the hull. It should be obvious that this type of watercraft is quite compact in its nature.
Because of the small size of this type of watercraft, it presents particular problems in connection with the exhaust treatment. That is, it is obviously necessary to discharge the exhaust gases from the powering internal combustion engine to the atmosphere. The discharge of the exhaust gases should be such, however, so that there is adequate cooling and silencing of the exhaust gases. In addition, the exhaust gases should be discharged in such a way as to not soil the hull of the watercraft, nor should the exhaust gases be discharged into proximity to the riders of the watercraft. Finally, the exhaust system should be designed so as to provide good tuning for the performance of the engine. All of these factors are difficult to accommodate in such small personal watercraft.
It is, therefore, a principal object of this invention to provide an improved exhaust system for a small personal watercraft.
It is a further object of this invention to provide an exhaust system for a personal watercraft that will provide sufficient length of exhaust gas flow so that the exhaust gases may be discharged to the atmosphere away from the occupants of the watercraft and also to provide adequate length for engine tuning purposes.
The engines employed for powering personal watercraft normally are liquid cooled. Coolant for the engine is drawn from the body of water in which the watercraft is operating and is discharged back into the body of water after being circulated through the engine. Frequently it is the practice to provide a cooling jacket around a portion of the exhaust system through which the engine coolant also passes. This cooling of the exhaust gases improves silencing and also provides protection for the hull from the heat of the exhaust system. One way in which the water from the cooling jacket is returned to the body of water in which the watercraft is operating is to mix it with the exhaust gases in the exhaust system and discharge the water along with the exhaust gases.
Although this type of coolant discharge further aids in exhaust silencing and water discharge, it raises the possibility that water may enter the engine through the exhaust system. This is obviously an undesirable result.
It is, therefore, a still further object of this invention to provide an improved exhaust system for a personal watercraft wherein at least a portion of the engine coolant is discharged along with the exhaust gases but wherein the exhaust system is constructed and configured so that water is not likely to flow to the engine through the exhaust system.
If all of the engine coolant is discharged back to the body of water in which the watercraft is operating through the exhaust system, then when running at high speeds and high loads, there may be excess back pressure in the exhaust system. The reason for this is that the amount of water circulated for cooling purposes increases generally with engine speed and frequently in a nonproportional manner. As a result, both the water flow and exhaust flow can increase as engine speed and load increases, and this can give rise to problems with excess back pressure.
It is, therefore, a still further object of this invention to provide an improved exhaust system for a small watercraft and water discharge system that incorporates at least in part the exhaust system.
These small personal watercraft generally are relatively simple in instrumentation and normally do not employ any coolant temperature sensor. As a result, it is difficult at times for the operator to assure that coolant is flowing through the cooling jacket of the engine. There have been proposed systems wherein a tell-tale is provided to enable the operator to ascertain that coolant is being circulated through the engine cooling jacket. These tell-tales discharge a portion of the coolant at a location where the operator can see it and confirm that water is flowing through the engine cooling jacket. However, the previously proposed tell-tales with this type of watercraft have certain disadvantages. Generally these tell-tales extend from the engine cooling system to a point on the upper side of the deck so as to be visible by the operator. However, this upwardly extending tell-tale conduit can cause water to remain in the conduit when the engine is not running. This can cause corrison and obstruction of the conduit, particularly when operating in a marine environment. Also, this upwardly location of the tell-tale outlet may cause some of the water to flow into the rider's area and collect on the floor there.
It is, therefore, a still further object of this invention to provide an improved tell-tale arrangement for a personal watercraft having a water-cooled engine.